Bird power.

[Wild-Woman]

Leading on from Nature's Great Events, something has crossed my mind and I'm hoping that an experienced biologist/physicist/ornithologist can explain to me how they do it. Basically, when a Bald Eagle, Sea Eagle, even our own Osprey, actually powers up enough a split second after they've grabbed a heavy weight fish like a salmon, from the water, away from the surface, bearing a fish that could almost be the same weight as the bird itself?
That's like me running and picking up weight, almost equal to my own and continuing until I find somewhere to put it down.
How do they suddenly compensate in that time? Does their brain 'know' how much to power up before they lift? Their co-ordination must be hugely more advanced than our own. Quite amazing.

Just to add. I've just looked up average weights.

Male Bald Eagle: 7-10 pounds
Female Bald Eagle: av 14 pounds
Salmon: up to 30 pounds!

[The Woodman]

Your wish hasn't come true Wild-Woman becauseI have none of the attributes you wish for in answering your question!

My thoughts are these.

Your analogy of you running and picking up a weight is exactly what any bird does. If we concentrate on the species of interest and the object is too heavy, the bird will leave it otherwise it risks becoming waterlogged or at the worst,drowned. It will learn at an early age to avoid the size of fish prey that it cannot lift for two reasons. The first is that it will not be able to generate the required amount of "lift" by its physical size and available energy. Secondly, it has to overcome the power of the fish whilst it's still in the water. A salmon of 30 lbs is a very powerful beast and more than capable of pulling an eagle underwater but when its in the air - that's another story.For this reason, the actual method of attack is critical.

Once the target is selected the bird approaches with talons extended forward and uses its momentum to assist lift and the talons swing like a pendulum removing the fish from its environment very quickly.

Imagine running up to a handbag on a pavement for example. Your experience will tell you that it should easily be lifted and you will not even have to think about it the process. You might have to stoop a little but your right arm will reach forward, your body will lift and you will continue in a hopefully smooth and graceful action!

Replace the bag with a cardboard box. It has no convenient handles and you have no idea how heavy it is. You will have to stop, assess its weight by a trial lift with two hands and carry on running if it is light enough to carry.

Your brain assesses the info very quickly and of course if the box is too big, heavy, awkward etc. you will leave it.

Our brains perform complex tasks just like eagles but we have the benefit of being able to use reasoning in the process.

I hope that makes a bit of sense.

[sunnydale]

Originally Posted by The Woodman

I hope that makes a bit of sense.

It does to me! I hadn't before considered what WW was asking and your response was very interesting and informative Woodman. Thanks.

[squishy]

it's like people walking. how do we know the exact amount of pressure to apply to each step, and how much grip it will have, and how to keep ourselves balanced? it's all sub-concious, and i'm sure thats the way it is for birds. (i'm not saying that flight isn't a marvel, just that the birds probably don't have to 'think' about it.)

[lol geoff]

Sounds good to me too and don't forget a fish in the water is probably half the weight of a fish in the air. Sometimes when you see films of Bald Eagles fishing quite often they will lift a fish but then drop it almost immediatley, although they must of had a good enough grip to get the fish out of the water in the first place. I remember also seeing footage of one swimming to the bank with a fish being unable to lift it and itself out of the water.

[Meta menardi]

It is not unknown for birds to drown after mis-judging the whole thing, I believe, but I guess you sort of get weeded out of the gene pool.

(Can you get weeded out of a pool?)

[diggleken]

Good question - and I dont know the answer scientifically, but at a guess - these birds have terrifically powerful wings to enable this lift and as others have said, they will have develped a judgement or learned , both personally and genetically, regarding what can be lifted.
If they get it wrong they will release the prey.
The Salmon record is around 64lbs by the way (or it was the last time I looked!)
most fish wont be anwhere near that of course and a 2lb fish is still a good size for eating, but not too heavy for these big birds.
They might also decide on size of prey depending how far away from the nest they are, for feeding young.
Which is why Osprey nest as close as they can to a good food source, be it loch or river.
Cheers
Ken

[Wild-Woman]

Originally Posted by The Woodman

Your wish hasn't come true Wild-Woman becauseI have none of the attributes you wish for in answering your question!

My thoughts are these.

Your analogy of you running and picking up a weight is exactly what any bird does. If we concentrate on the species of interest and the object is too heavy, the bird will leave it otherwise it risks becoming waterlogged or at the worst,drowned. It will learn at an early age to avoid the size of fish prey that it cannot lift for two reasons. The first is that it will not be able to generate the required amount of "lift" by its physical size and available energy. Secondly, it has to overcome the power of the fish whilst it's still in the water. A salmon of 30 lbs is a very powerful beast and more than capable of pulling an eagle underwater but when its in the air - that's another story.For this reason, the actual method of attack is critical.

Once the target is selected the bird approaches with talons extended forward and uses its momentum to assist lift and the talons swing like a pendulum removing the fish from its environment very quickly.

Imagine running up to a handbag on a pavement for example. Your experience will tell you that it should easily be lifted and you will not even have to think about it the process. You might have to stoop a little but your right arm will reach forward, your body will lift and you will continue in a hopefully smooth and graceful action!

Replace the bag with a cardboard box. It has no convenient handles and you have no idea how heavy it is. You will have to stop, assess its weight by a trial lift with two hands and carry on running if it is light enough to carry.

Your brain assesses the info very quickly and of course if the box is too big, heavy, awkward etc. you will leave it.

Our brains perform complex tasks just like eagles but we have the benefit of being able to use reasoning in the process.

I hope that makes a bit of sense.

Thanks TW. That does makes sense to me. A really understandable explanation, which I am now digesting.
I was never any good at physics.